JP6482730B2 - Wireless communication system - Google Patents

Description

  The present invention relates to a wireless communication system, and is applicable to, for example, a wireless system using a MIMO transmission technology that transmits and receives a plurality of streams using a plurality of antennas.

  In recent years, mobile communication traffic has been steadily increasing due to higher functionality of mobile phones, and it has been required to realize further high-speed wireless communication in a limited frequency band. One of the implementation methods is MIMO (Multiple-Input Multiple-Output) transmission technology (for example, JP-A-2014-131181). In MIMO transmission, a plurality of signal sequences are transmitted at the same frequency from a plurality of transmission antennas at the same time, and are spatially multiplexed. By using a multipath environment between each transmission antenna and each reception antenna, each signal is separated and decoded by performing signal processing on the receiver side. Accordingly, the transmission path capacity can be increased in proportion to the number of transmission / reception antennas without increasing the frequency bandwidth to be used, that is, the frequency utilization efficiency can be improved. In mobile communication, which is an out-of-line communication system, a receiver receives a plurality of signals by reflection from the surroundings. This propagation environment fluctuates in time depending on the movement of a moving object using the system or an object causing scattering around the system. When using multiple antennas that are spaced apart so that these propagation environments can be regarded as independent, this is equivalent to the existence of multiple transmission paths, and multiple independent signals corresponding to the number of antennas in the same frequency band. Can be transmitted.

  Under the situation where the radio frequency of the microwave band is tight with the increase in traffic of mobile communication, for example, an increase in transmission capacity using a high frequency band such as a millimeter wave band is required. Compared to millimeter wave communication and microwave communication, millimeter wave communication has the advantage of being able to handle relatively wide-band signals and is suitable for large capacity, but it is difficult to amplify large power and propagation loss. There is a demerit that the communication distance is shortened because of the large. As a countermeasure, there is a beam forming technique that performs spatial synthesis using a plurality of antenna elements. This is a technique for controlling the phase of a transmission signal output from a plurality of antenna elements on the transmission side so as to achieve in-phase combining that maximizes power at the receiver. As the number of antenna elements increases, the directivity of the main lobe becomes sharper, and the side lobes in other directions are attenuated. The antenna element spacing is suitably λ / 2 (λ: wavelength), and a relatively small antenna unit can be realized in the millimeter wave band with a short wavelength.

JP 2014-131181 A

  However, if the directivity is strengthened by the beam forming technique, it will be difficult to coexist with MIMO transmission. Since the line-of-sight communication becomes impossible and a sufficient multipath cannot be obtained, the correlation between signals transmitted from a plurality of antennas is large. Therefore, it cannot be considered that there are a plurality of transmission paths, and a transmission capacity proportional to the number of antennas cannot be expected.

In the fifth generation mobile communication system, a transmission rate of 10 Gbps is set as the target around 2020. In order to achieve the goal, it is indispensable to achieve both broadband and MIMO transmission technology, and a technology for realizing it is desired.
An object of the present disclosure is to provide a wireless loss system suitable for MIMO transmission.
Other problems and novel features will become apparent from the description of the specification and the accompanying drawings.

An outline of typical ones of the present disclosure will be briefly described as follows.
That is, the wireless communication system includes a first wireless device having a plurality of antennas for performing wireless communication and a second wireless device having a plurality of antennas, and the first wireless device and the second wireless device. At least one radio selects two antennas from three or more antennas and performs 2 × 2 MIMO communication. A signal vector transmitted from the i-th and j-th transmitting antennas of the first radio on an orthogonal plane obtained by orthogonal detection or demodulation of the received signal of the k-th receiving antenna of the second radio. The angle is φ1, and the signals received from the l-th receiving antenna of the second radio are transmitted from the i-th and j-th transmitting antennas of the first radio on an orthogonal plane obtained by quadrature detection or demodulation. The angle formed by the signal vector is φ2, the absolute value of the angle obtained by subtracting φ2 from φ1 is φ, and the transmission antenna and the reception antenna that are the closest to π radians are selected.

  According to the radio communication system, the transmission rate can be improved.

Diagram for explaining a MIMO wireless communication system The figure for demonstrating the phase relationship of the received signal when a radio | wireless machine moves The figure for demonstrating the phase relationship of the received signal when a radio | wireless machine moves The figure for demonstrating an example of the antenna arrangement | positioning of a radio | wireless machine The figure for demonstrating the other example of antenna arrangement | positioning of a radio | wireless machine The figure for demonstrating the synthetic | combination phase error in the antenna arrangement | positioning of FIG. 3B The figure for demonstrating the synthetic | combination phase error in the antenna arrangement | positioning of FIG. 3A The figure which shows the coordinate system of FIG. 4A, 4B The figure for demonstrating the structure of the antenna which concerns on an Example. The figure for demonstrating the structure of the antenna which concerns on an Example. The figure which shows the characteristic at the time of applying the antenna of FIG. 5B to a base station antenna The figure which shows the characteristic at the time of applying the antenna of FIG. 5B to a mobile station antenna The figure for demonstrating the antenna selection based on an Example The figure for demonstrating the antenna selection based on an Example Example of OFDM signal The figure which shows the amount of CNR degradation with respect to a synthetic | combination phase error The figure for demonstrating the effect of the radio system which concerns on an Example The figure for demonstrating the effect of the radio system which concerns on an Example The figure for demonstrating the effect of the radio system which concerns on an Example The figure which shows the structure of the radio | wireless communications system which concerns on an Example.

  First, the MIMO wireless communication system will be described with reference to FIG.

  The wireless communication system 100 includes a first wireless device 110 and a second wireless device 120. The first radio 110 has a first antenna (ANT1) and a second antenna (ANT2). The second radio 120 includes a third antenna (ANT3), a fourth antenna (ANT3), phase shifters (π / 2 units) 121 and 122, and adders 123 and 124.

  As shown in FIG. 1, in the MIMO technology in line-of-sight communication, when the radio frequency of wavelength λ, the transmission distance, and the antenna interval (dAnt) satisfy the following conditions, it can be regarded as a plurality of independent communication paths. Are known techniques.

In the wireless communication system 100, it is assumed that the transmission distance is R, the distance between the first antenna (ANT1) and the third antenna (ANT3) is D13, and the distance between the second antenna (ANT2) and the fourth antenna (ANT4) is d24. , For R = d13 = d24, signals transmitted from the two first antennas (ANT1) and the second antenna (ANT2) on the transmission side are transmitted to the third antenna (ANT3) and the fourth antenna (ANT4) on the reception side. The antenna installation interval is dAnt so that the transmission path difference when receiving at λ / 4 is λ / 4, and the phase difference between the signal (S1) and the signal (S2) transmitted from the two antennas is π / 2. To do. When combining the signals of the two receiving antennas, one of the phase shifters 121 and 122 rotates the phase so that one emphasizes S1 and cancels S2, and the other emphasizes S2 and cancels S1. The signals can be separated into two signals (D1, D2) by combining them at 123 and 124. The optimal condition for complete separation can be obtained by the following equation.
d13 = d24
d14 = d23
d14 = d13 + λ / 4
d23 = d24 + λ / 4
dAnt = (d14 ² −d13 ² ) ^1/2
In particular, since the wavelength λ is short in the millimeter wave, it can be realized with a practical antenna interval of several centimeters to several meters.

  In the case of fixed communication, the antenna arrangement according to the propagation distance can be designed in advance, but in the case of mobile communication, the distance between the radios changes due to the movement of one or more radios. It is impossible.

  Next, the phase relationship of the received signal when the wireless device moves will be described with reference to FIGS. 2A and 2B. FIG. 2A shows an example of an ideal synthesis, and FIG. 2B shows an example of a case where the amplitude after signal separation attenuates. Case 1 in FIG. 2A is equivalent to FIG. Point (a) in FIG. 1 corresponds to (a) in FIGS. 2A and 2B, and is a vector indicating the phase relationship received by the third antenna (ANT3) and the fourth antenna (ANT4). The vector of the received signal is determined by the relationship between the wavelength of d13, d14, d23, and d24, which are distances formed by the first antenna (ANT1), the second antenna (ANT2), the third antenna (ANT3), and the fourth antenna (ANT4). . The point (b) in FIG. 1 is indicated by a dotted line in FIGS. 2A and 2B (b), and is a vector whose phase is adjusted by the phase shifters 121 and 122 in order to separate the signals. A point (c) in FIG. 1 is indicated by a solid line in FIGS. 2A and 2B (c), and is a vector obtained by combining the signals in (b). Case 1 to case 3 in FIG. 2A is an ideal synthesis, and the amplitude of the signal is doubled in (c). The signal amplitude after the separation of the case4 to case6 signals in FIG. 2B is reduced, that is, the S / N ratio is reduced, so that the signal quality is deteriorated. In the worst case, the signal cannot be separated as shown in case 6, so the MIMO effect of increasing the transmission capacity cannot be obtained. Therefore, one signal sequence must be sent.

  The radio communication system according to the embodiment selects an antenna suitable for MIMO transmission from a plurality of transmission antennas and / or a plurality of reception antennas. When the conditions for MIMO (multi-stream) transmission are not satisfied, switching to single signal sequence (single stream) transmission is performed.

  According to the present embodiment, it is possible to improve the transmission speed by selecting the optimum two from three or more antennas and suppressing signal quality degradation in multi-stream transmission for line-of-sight communication. Also, when the conditions for transmitting multi-streams are not satisfied, the optimum transmission rate can be realized by switching to single-stream transmission.

  In this specification, a unit for transmitting and receiving one stream is denoted as “antenna”, and a unit for performing beamforming is denoted as “antenna element”. An “antenna” that transmits a beamformed signal is composed of a plurality of “antenna elements”. The unit handled in the MIMO transmission is an “antenna”.

  Examples will be described below with reference to the drawings. However, in the following description, the same components may be denoted by the same reference numerals and repeated description may be omitted.

  First, the radio | wireless communications system which concerns on an Example is demonstrated using FIG. FIG. 11 is a block diagram illustrating the wireless communication system according to the embodiment. The wireless communication system 100 according to the embodiment has the same configuration as that of the wireless communication system 10 of FIG.

Next, a method for selecting two from three or more antennas will be described. Assume that the number of antennas of the first radio 110 is M, and the number of antennas of the second radio 120 is N. Here, it is assumed that the conditions of M ≧ 2, N ≧ 2, and M + N ≧ 5 are satisfied. For the sake of explanation, consider the case where the first radio 110 is transmitting and the second radio 120 is receiving. The angle formed by the signal vector transmitted from the i-th antenna (ANTi) and the j-th antenna (ANTj) of the first radio 110 in the received signal of the k-th antenna (ANTk) of the second radio 120 Is set to φ1. The angle formed by the signal vector transmitted from the i-th antenna (ANTi) and the j-th antenna (ANTj) of the first radio 110 in the received signal of the l-th antenna (ANTl) of the second radio 120. Is set to φ2.
Φ (i, j, k, l) = abs (φ1-φ2) Equation (1)
Are calculated for all combinations of transmitting antennas (ANTi, ANTj) and receiving antennas (ANTk, ANTl). Here, abs () is an absolute value. The combination of the transmitting antenna and the receiving antenna that is closest to π is selected from all Φ.

  7A and 7B are diagrams illustrating an example of antenna selection. A transmission signal (Si) of the i-th transmission antenna (ANTi) and a transmission signal of the i-th transmission antenna (ANTj) are provided in the k-th reception antenna (ANTk) and the l-th reception antenna (ANTl). (Sj) is spatially synthesized and received. For each case, Φ is calculated using equation (1). Here, the counterclockwise direction is the phase advance (+), and the clockwise direction is the phase delay (−). Further, 2π = 0, π = −π, etc. are used. 7A and 7B, Φ (case1) = Φ (case2) = Φ (case3) = π, Φ (case4) = 2π / 3, Φ (case5) = π / 3, Φ (case6) = 0, and case1 or Select either case2 or case3.

  The vectors of the received signals shown in FIGS. 7A and 7B are obtained after orthogonal detection in the case of single carrier transmission, after despreading in the case of CDMA (Code Division Multiple Access), and after demodulation in the case of OFDM (Orthogonal Frequency Division Multiplexing). Expressed in Cartesian coordinate system. In order to obtain a received signal vector on the receiving side, it is only necessary to transmit known signals orthogonal (independent from each other) in the frequency or time domain from the transmitting antenna. As an example of this signal, a channel estimation pilot signal used in MIMO transmission is used.

  FIG. 8 is a diagram illustrating an example of an OFDM signal. In the OFDM signal, a pilot signal (pilot symbol) of several symbols is inserted for each data symbol of several symbols to several tens of symbols. The pilot signal is used for transmission path estimation and synchronous detection. As for the A subcarrier of the pilot signal, only the A-th antenna (ANT (A)) transmits pilot data, and the other antennas are set to 0. Similarly, for the B subcarrier of the pilot signal, only the B-th antenna (ANT (B)) transmits pilot data, and the other antennas are set to zero. Thereafter, the same processing as C, D,... Is performed. In the pilot signal, since there is no interference signal, the real component (I) and the imaginary component (Q) obtained by performing the complex Fourier transform are directly used as vectors such as Si and Sj. Different data symbols are transmitted from the selected two antennas. Information thus obtained on the receiving side is transmitted to the transmitting side as antenna selection control information, and the transmitting side transmits using an antenna based on the control information. In the case of TDD (Time Division Duplex), when the time is sufficiently short, the transmission / reception conditions are the same, and therefore the antenna can be selected without having to transmit control information.

  As the number of antennas increases, the probability that a multi-stream can be transmitted increases, but the improvement efficiency gradually decreases as the number of antennas increases. Therefore, there are cases where a multi-stream cannot be sent with a realistic number of antennas (such as case 6 in FIG. 7B). In this case, it is desirable to send a single stream because signal separation is impossible and the error rate is greatly degraded.

FIG. 9 is a diagram showing the amount of CNR degradation with respect to the combined phase difference. The horizontal axis represents the combined phase error, and 0 ° is the case where the image is ideally combined (the combined phase difference is 0 ° when Φ is π, and the combined phase difference is 180 ° when Φ is 0). The composite phase error is obtained from the best Φ calculated for antenna selection, and the C / N degradation amount is subtracted from the C / N in the case of a single stream. When the result is larger than the required C / N: Th _{C / N, a} multi-stream is transmitted, and when it is smaller, a single stream is transmitted. Here, C / N in the case of a single stream is measured by an independent pilot symbol. Therefore, the C / N of single signal transmission is determined by a transmission signal whose information is known, independent of frequency or time at each transmission antenna.

Also, since the required C / N varies depending on the multi-value number of quadrature amplitude modulation (QAM), a threshold Th _nQAM is provided for each multi-value number n (n = 16, 64, 256, etc.) to improve efficiency by performing adaptive modulation. You can also.

  Next, the effect of the present embodiment will be described with reference to FIGS. FIG. 10A is a diagram showing transmission distance versus transmission speed (number of bits / carrier). FIG. 10B is a diagram showing transmission distance versus transmission speed (average number of bits / carrier). FIG. 10C is a diagram showing transmission distance versus transmission speed (average transmission rate ratio). 10A to 10C compare the case of MIMO (multi-stream) and reception diversity (single stream) with two reception antennas. The total number of antenna elements for MIMO and receive diversity was made equal. The radio wave loss in free space was assumed according to the transmission distance on the horizontal axis. The modulation method is quadrature amplitude modulation, and adaptive modulation is performed to optimize the multi-value number according to the CNR (Carrier to Noise power Ratio) of the receiver. Compared with C / N determined by the multi-value number of quadrature amplitude modulation, the multi-value number is determined as the maximum multi-value number that can be transmitted. In the case of OFDM, the vertical axis in FIGS. 10A to 10C is a value per subcarrier.

  FIG. 10A shows a case of fixed communication, in which an optimum antenna interval can be designed according to the propagation distance. First, focus on reception diversity. When the propagation distance is doubled, the CNR is reduced by about 6 dB. The difference between the required CNRs of multi-valued numbers (for example, 256QAM and 64QAM) corresponding to the difference of 2 bits by adaptive modulation is about 6 dB. Therefore, focusing on the fact that the number of bits per carrier is reduced by 2 bits, the propagation distance at the point where 64QAM becomes 16QAM is twice the propagation distance at the point where 256QAM becomes 64QAM, and the propagation distance at the point where 16QAM becomes QPSK is 64QAM. Is double the propagation distance of 16QAM. Next, focus on MIMO. In MIMO, two different transmission signals can be transmitted, so the number of bits per carrier is doubled compared to the reception diversity. However, since the total number of antenna elements is made equal, the spatial synthesis gain per stream is -6 dB compared to the reception diversity, and therefore the propagation distance is a multivalued number in MIMO in which the propagation distance is ½ compared to the reception diversity. It can be seen that the effect is obtained under the condition of 16 or more.

  FIG. 10B shows the case of mobile communication. The number of antennas is two for both the base station and the mobile station. The vertical axis represents the average number of bits, and in the case of reception diversity, it is equal to FIG. 10A. The antenna spacing in the case of MIMO is designed to be optimal at a transmission distance capable of transmitting 256QAM, that is, at a location relatively close to the base station. In MIMO, in addition to the propagation loss, the CNR deteriorates due to the combined phase error, so the average number of bits is smaller than the MIMO in FIG. 10A. It can be confirmed that the average number of bits is improved by selecting the number of transmission streams (MIMO: 2 streams, reception diversity: 1 stream).

  FIG. 10C shows a case where the antenna selection of this embodiment is applied. The horizontal axis represents the propagation distance, and the vertical axis represents the transmission rate ratio of MIMO with respect to reception diversity, and the average transmission rate ratio obtained by averaging the distance between the base station (BS) and the mobile station (MS) within the horizontal axis. “Select number of streams” in FIG. 10B is the same as “No antenna selection” in FIG. 10C. BS: 2/3 antenna selection, MS: 2/3 antenna selection, BS, MS: 2/3 antenna selection is 2 × 2 (2 outputs with 2 inputs) MIMO by selecting the best antenna at BS or MS or both Is the case. When selecting two antennas for the BS and the MS, it is better to select the BS antenna. This is because the MS has a small antenna interval in consideration of a small machine such as a mobile phone, and therefore, the selection of a BS antenna that can have a relatively large antenna interval increases the probability that the combined phase error will be small. Focusing on the effect of the transmission rate of 1.5 times, it can be seen that if two antennas are selected from three antennas in the BS and MS, the transmission distance can be doubled compared to the case where no antenna is selected.

  Next, the antenna arrangement of the wireless device according to the embodiment will be described with reference to FIGS. 3A and 3B. 3A and 3B are diagrams illustrating an antenna arrangement of the radio device according to the embodiment. In order to perform beam forming, it is composed of a plurality of antenna elements. FIGS. 3A and 3B are examples, and in one MIMO antenna unit, 64 elements (= 8 × 8) are arranged at intervals of a half wavelength λ / 2. FIG. 3A shows an example in which the antenna units are arranged in the horizontal direction (parallel to the ground), and FIG. 3B shows an example in which the antenna units are arranged in the height direction (perpendicular to the ground).

  The antenna arrangement direction and the combined phase error will be described with reference to FIGS. 4A, 4B, and 4C. 4A shows a combined phase error when the antenna is arranged in the vertical direction (arrangement of FIG. 3B), and FIG. 4B shows a combined phase error when the antenna is arranged in the horizontal direction (arrangement of FIG. 3A). FIG. 4C is a diagram showing the coordinate system of FIGS. 4A and 4B. A base station with a fixed antenna position and a mobile station (such as a mobile phone) whose antenna position changes are assumed. As shown in FIG. 4C, a line connecting the base station and the mobile station is placed on the X axis and is parallel to the ground. A direction parallel to the ground and perpendicular to the X axis is placed on the Y axis. A direction perpendicular to the XY plane (perpendicular to the ground) is placed on the Z axis. 4A and 4B represents the angle θ (± 180 °) on the XY plane of the fourth antenna (ANT4) when the third antenna (ANT3) of the mobile station is fixed at the origin. 4A and 4B represents the angle φ (± 90 °) between the fourth antenna (ANT4) and the XY plane when the third antenna (ANT3) of the mobile station is fixed at the origin. The ideal composition approaches a light color, and if it cannot be separated, it approaches a dark color. Since the data is acquired so that the position of the fourth antenna (ANT4) has a uniform distribution, FIG. 4 has a shape close to an ellipse. 4A and 4B have different characteristics because the positional relationship between the second antenna (ANT2), the third antenna (ANT3), and the fourth antenna (ANT4) changes.

  Next, the configuration of the antenna of the wireless device according to the embodiment will be described with reference to FIGS. 5A and 5B. FIG. 5A is a diagram showing an antenna configuration. FIG. 5B is a diagram showing a subarray configuration. In this embodiment, an antenna configuration of 256 elements (16 × 16) as shown in FIG. 5A is used, and a subarray configuration of 64 elements (8 × 8) as shown in FIG. 5B is used (4 subarrays as an example). Therefore, the antenna (ANT) includes a subarray antenna A, a subarray antenna B, a subarray antenna C, and a subarray antenna D. Of these, two antennas that are close to ideal synthesis are selected and transmitted.

  6A and 6B are diagrams for explaining the effect of the subarray antenna. FIG. 6A shows the characteristics when two sub-array antennas A, B, and C in FIG. 5B are selected as the base station antenna. It can be seen that the probability of being able to send a multi-stream is greatly increased because antennas close to the ideal combination of FIGS. 4A and 4B are selected and the combinations of subarray antennas B and C of FIG. 5B are also increased. . FIG. 6B shows characteristics when two mobile station antennas are selected from the sub-array antennas A, B, and C. It can be seen that results similar to those of the base station antenna are obtained. This result is an example in which the radio frequency is considered as the millimeter wave band, the base station antenna interval is several tens of centimeters to several meters, and the mobile station antenna is several centimeters to several tens of centimeters in consideration of the small size. It is desired to design appropriately according to the radio frequency and transmission distance as in the past.

  When the mobile station is a small wireless device such as a mobile phone, the position of the antenna is freely arranged in a three-dimensional space. Therefore, it is apparent from FIGS. 4A and 4B and FIGS. 6A and 6B that the effect of antenna selection is increased by arranging both in a linear direction in the horizontal direction or in the vertical direction with respect to the ground instead of in a single direction. In this embodiment, this is realized by configuring the subarray antenna in the horizontal and vertical directions.

  The effect of the present embodiment is increased by flexibly configuring the antenna elements to be used, not limited to the subarray antenna. In addition, since the number of antenna elements that transmit the same signal can be freely selected, the power can be easily adjusted by increasing the number of antenna elements when sending a single stream, that is, by increasing the number of spatial synthesis. . Furthermore, by giving an appropriate phase difference to the signal input to each antenna element, it is possible to easily control the direction of the beam directivity according to the position of the mobile station.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiments. However, the present invention is not limited to the above-described embodiments, and needless to say, various modifications can be made.

DESCRIPTION OF SYMBOLS 10 ... Wireless communication system 100 ... Wireless communication system 110 ... 1st radio | wireless machine 120 ... 2nd radio | wireless machine 121 ... Phase shifter 122 ... Phase shifter 123 ... Adder 124 ... Adder

Claims (6)

A first wireless device having a plurality of antennas for wireless communication and a second wireless device having a plurality of antennas;
At least one of the first radio and the second radio selects two antennas from three or more antennas, performs 2 × 2 MIMO communication,
A signal vector transmitted from the i-th and j-th transmitting antennas of the first radio on an orthogonal plane obtained by orthogonal detection or demodulation of the received signal of the k-th receiving antenna of the second radio. The angle is φ1, and the signals received from the l-th receiving antenna of the second radio are transmitted from the i-th and j-th transmitting antennas of the first radio on an orthogonal plane obtained by quadrature detection or demodulation. A wireless communication system that selects φ2 as the absolute value of the angle obtained by subtracting φ2 from φ1 and selects the combination of the transmitting antenna and the receiving antenna where φ is closest to π radians. In claim 1,
C obtained from the value of Φ closest to π radians from C / N of a single signal transmission obtained by a transmission signal whose information is known, independent of frequency or time, at each transmission antenna of the first radio. When the C / N during MIMO communication that can be calculated by subtracting the / N degradation amount is smaller than a predetermined C / N that is set based on the multilevel number of quadrature amplitude modulation, wireless communication is performed as single signal transmission. system. In claim 2,
The majority value of the quadrature amplitude modulation is determined to be the maximum number of multivalues that can be transmitted, compared with the C / N determined by the number of quadrature amplitude modulation values, and the predetermined C / N is the minimum number of multivalues. C / N wireless communication system. In any one of Claims 1-3,
A wireless communication system that uses a three-dimensional antenna to give directivity to a transmission signal or a reception signal, and changes the position of the antenna by a combination of both horizontal and vertical. In any one of Claims 1-3,
In order to give directivity to the transmission signal or the reception signal, a multi-element antenna is used,
A wireless communication system that changes the position of an antenna according to a combination of elements used for transmission or reception. In claim 4,
In order to give directivity to the transmission signal or the reception signal, a multi-element antenna is used,
A wireless communication system that changes the position of an antenna according to a combination of elements used for transmission or reception.

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